Various patents disclose methods and apparatus for blow or vacuum forming, filling, and sealing a container. See, for example, Weiler U.S. Pat. No. 3,597,793, Komendowski U.S. Pat. No. 3,919,374, Weiler et al. U.S. Pat. No. 4,176,153, Weiler et al. U.S. Pat. No. 4,178,976, Hansen U.S. Pat. Re. No. 27,155 and patents cited therein. This type of apparatus needs to be sterilized for aseptic filling of products.
Machines of the type disclosed in the aboveidentified patents may be advantageously used for packing of liquid products used in pharmaceuticals, medical devices, diagnostic processes, dentistry, nd food products. It is typically desirable, if not necessary, to form, fill, and seal containers of such fluids in a manner which keeps the container and contents free of microorganisms and other contaminants. To this end, a sterilizing agent, such as vapor having a transferable latent heat (e.g., steam) is typically utilized to sterilize the flow passages in the machine components prior to starting the production packaging operations.
Sterilization is necessary when the machine is shut down after being used with one product before switching to a second product. Even when the machine is shut down between filling operations with the same product, sterilization may be necessary or desired because contaminants can enter the machine components during shut down periods when the machine is not operating at above-atmospheric internal pressures.
A steam sterilizing system incorporated in a liquid packaging machine is disclosed in commonly owned Weiler et al. U.S. Pat. No. 4,353,398. The steam sterilization system described in that patent is designed to be connected to a source of sterilizing steam and includes two major flow paths for the sterilizing steam. One flow path directs the sterilizing system through the liquid product fill or supply lines. A second flow path directs the sterilizing steam through the process gas supply lines (e.g., lines for supplying pressurized air for blow molding the container). The two main sterilizing steam flow paths are isolatable from each other.
In the sterilizing operation disclosed in Weiler et al. U.S. Pat. No. 4,353,398, the liquid product lines are first opened to the sterilizing steam while the gas lines are isolated from the sterilizing steam. The product lines are sufficiently sterilized after the sterilizing steam has flowed through the product lines for about 30 minutes. Next, the product lines are isolated from the sterilizing steam, and the gas lines are opened to the sterilizing steam for about 15 minutes.
Although the sterilizing process disclosed in the above-discussed Weiler et al. U.S. Pat. No. 4,353,398 works well for applications for which it was designed, it has been found that it would be desirable to provide a process for effectively sterilizing the fluid product lines and gas lines within a shorter period of time and utilizing a single flow path for the sterilizing steam. This would result in a more efficient operation of the automatic packaging machine.
In an automatic packaging machine of the form-filled-seal type, the liquid product fill system and the gas supply system each typically include one or more filters and other components. Certain components, especially certain types of filters, can be damaged when subjected to an excessive pressure differential, especially at the termination of a system sterilization process when the reduced pressure produced as the sterilizing steam condenses can generate a reduced pressure differential across a portion of the system that could damage some types of filters.
Specifically, after sterilizing steam has flowed through a system for a sufficient time to effect proper sterilization, the shutting off of the steam flow permits the system to cool. The remaining steam in the system condenses during the cooling. As the steam condenses, the pressure within the system is reduced. Indeed, the system pressure may be reduced to below the ambient external pressure so as to, in effect, create a sub-atmospheric pressure within portions of the system.
The pressure reduction in the system caused by the condensing steam could result in a differential pressure across a portion of the system, including across a filter. An excessive differential pressure across the filter is likely to damage the system filters. Inasmuch as the capability of some types of filters to withstand a differential pressure decreases with increasing temperature, such filters are particularly vulnerable to damage in the immediate post-sterilization (i.e., cool-down) time period.
Further, the sub-atmospheric pressure in the system could result in the ingress of bacteria or other contaminants carried by the relatively higher pressure ambient atmosphere that may leak into the system.
In view of the potential contamination problem and in view of the potential damage problem with respect to filters and other components as the sterilization process is terminated, it would be desirable to provide an improved sterilization process that would maintain the systems at pressures greater than atmospheric and that would minimize pressure differentials.
It would also be advantageous if such an improved system could be provided with the capability for automatically accommodating the operation of the sterilization process throughout a range of pressures and for responding to a wide range of potential differential pressures. To this end, it would also be beneficial if such an improved process could be adapted for control in response to one or more process parameters, such as cycle time or system pressure. This would provide the user with a desirable selectivity of operational alternatives.
The sterilization process using steam to heat the components of the filling machine must be effected for a time period sufficient to effectively sterilize the component surfaces. The above-discussed U.S. Pat. No. 4,353,398 discloses a conventional sterilizing method wherein the sterilizing steam is controlled to flow through the system for a predetermined time interval. Although this works well in systems for which the steam sterilizing process is particularly designed, test runs must be made to provide temperature measurement data for use in designing the process to ensure that the system is subjected to a heat up period of sufficient duration to raise the temperature of the components to a proper sterilizing temperature at the beginning of the sterilizing interval.
The length of time that it takes components in a system to reach a predetermined elevated sterilizing temperature depends on, among other things, the component material and mass. Thus, once such a particular sterilization process has been conventionally designed for a particular system, it cannot be readily used with other systems or even with the same system for which it was designed if components of that system are changed. Accordingly, it would be desirable to provide an improved sterilization system that could effectively sense and register the temperature of one or more of the system components. Further, it would be advantageous if such an improved sterilization system could be provided with a control system for automatically controlling the introduction of steam to the components to be sterilized and for maintaining the flow of steam for a predetermined time interval after at least one selected component has reached a predetermined, elevated, sterilizing temperature.